In the art of making positive plates of the tubular type for use in lead-acid batteries it is customary to provide a grid structure which includes a top bar having a plurality of current collecting spines depending therefrom and a post or burning lug means. Also included in this tubular type plate is active material, a plurality of tubes which are arranged to confine the active material around the spines and a bottom bar for closing the bottoms of the tubes.
The common practice is to provide for the tops and bottoms of tubes having a so-called interference fit with the spines and top bar and the spines and bottom bar surfaces. In the case of the tube tops, the spines at their point of junction with the top bar are formed with enlarged portions over which the tube tops are engaged to provide an interference fit. Similarly, the bottom bar is formed with insert portions having openings into which the bottoms of the spines are pressed to form a lower interference fitted relationship of parts. Enlarged insert portions of the bottom bar may be engaged within the tube bottoms to provide a further interference fit.
Plates of the construction described may, in some cases, fail to adequately constrain the active material during operation of the battery. Swelling of the active material (which constantly takes place) may exert forces against inner wall portions of the tops and bottoms of the tubes. These forces may be greater than the holding forces of the interference fits at the tube ends with the result that gaps may be formed at tops and bottoms of the tubes allowing active material to escape.